A case of primary leiomyosarcoma of the ovary in a perimenarchal female is presented. Previous to this report, ovarian leiomyosarcoma was thought to arise predominantly in postmenopausal women and, indeed, this is the first reported case in a pubertal adolescent. The sarcoma was associated with bilateral cellular ovarian leiomyomas, suggesting malignant degeneration of such tumors. After complete resection, the patient is alive without evidence of recurrent disease 20 months after diagnosis. A review of the literature suggests that chemoradiation is of unproven benefit and aggressive surgical management is recommended.